fix(core-transactions): version 1 multi-signature handler should check milestone data

[bertiespell]

Summary

The MultiSignatureRegistrationTransactionHandler (version 1) was always returning false for .isActivated() - this PR updates it to instead check milestones.

Fixes #3866. Stops DeactivatedTransactionHandlerError from being thrown while syncing with devnet.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

Merging #3871 into develop will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #3871   +/-   ##
========================================
  Coverage    92.18%   92.18%           
========================================
  Files          620      620           
  Lines        14850    14850           
  Branches      1844     1844           
========================================
  Hits         13690    13690           
  Misses         948      948           
  Partials       212      212           

Flag	Coverage Δ
#functional	6.47% <0.00%> (ø)
#integration	9.56% <0.00%> (ø)
#unit	90.60% <100.00%> (ø)

Impacted Files	Coverage Δ
...s/src/handlers/one/multi-signature-registration.ts	96.15% <100.00%> (ø)

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